The present invention relates to a hydraulic valve lift device for internal combustion engine and, more particularly, to a hydraulic valve lift device adapted for relaxing impacts at the time of setting of the valve.
There have been proposed various types of valve lift devices for varying the valve or timing in accordance with load imposed on the engine or running speed of the engine. One of these known devices, which is basically identical to a known hydraulic tappet device, the oil in an oil chamber pressurized by a plunger engaging a push rod and by a lifter body is allowed to be relieved to the outside through a restriction or orifice so as to reduce the volume of the oil chamber, thereby to change the lift of the plunger.
In this valve lift device, the cam contour is two dimensional, and it is not necessary to change relative positions of the cam shaft and the plunger to each other, so that the construction of the device is considerably simple. However, since the device is constructed to vary the valve lift by relieving the oil from the oil chamber, it is impossible to make the cam have such a cam contour involving a curvature for reducing the movement of the intake and exhaust valves at the instant of seating as in the cam commonly used in engines. Therefore, a large impact force acts on the valve at the time of seating, generating a large noise and causing various inconveniences on the durability of the valve mechanism.